U.S. patent application number 10/689676 was filed with the patent office on 2004-04-29 for awakening level estimation apparatus for a vehicle and method thereof.
This patent application is currently assigned to Fuji Jukogyo Kabushiki Kaisha. Invention is credited to Oyama, Hajime.
Application Number | 20040080422 10/689676 |
Document ID | / |
Family ID | 32064330 |
Filed Date | 2004-04-29 |
United States Patent
Application |
20040080422 |
Kind Code |
A1 |
Oyama, Hajime |
April 29, 2004 |
Awakening level estimation apparatus for a vehicle and method
thereof
Abstract
An awakening level estimation apparatus for vehicle has: a
signal processing part; a frequency component amount calculation
part for calculating an average value of the frequency component
powers and calculating a maximum value of the frequency component
powers; a correction factor calculation part for calculating a high
frequency percentile value and calculating a low frequency
percentile value and calculating a correction factor; an evaluation
value calculation part for calculating an evaluation value; and a
decision part for deciding an awakening level of a driver.
Inventors: |
Oyama, Hajime; (Tokyo,
JP) |
Correspondence
Address: |
MCGINN & GIBB, PLLC
8321 OLD COURTHOUSE ROAD
SUITE 200
VIENNA
VA
22182-3817
US
|
Assignee: |
Fuji Jukogyo Kabushiki
Kaisha
Tokyo
JP
|
Family ID: |
32064330 |
Appl. No.: |
10/689676 |
Filed: |
October 22, 2003 |
Current U.S.
Class: |
340/576 ;
180/271 |
Current CPC
Class: |
G08B 21/06 20130101 |
Class at
Publication: |
340/576 ;
180/271 |
International
Class: |
G08B 021/06 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 23, 2002 |
JP |
P. 2002-308086 |
Claims
What is claimed is:
1. An awakening level estimation apparatus for vehicle comprising:
a signal processing part for calculating each frequency component
power by making frequency conversion of a displacement amount of a
vehicle in a direction of vehicle width detected in a time series
manner; a frequency component amount calculation part for
calculating an average value of the frequency component powers
calculated by the signal processing part as a high frequency
component amount and also calculating a maximum value of the
frequency component powers within a predetermined frequency domain
including a stagger frequency to become apparent in a state in
which an awakening level of a driver decreases as a low frequency
component amount; a correction factor calculation part for
calculating a high frequency percentile value in which the
proportion of the total sum to the sum of incidences counted from
the lower frequency component powers results in a predetermined
proportion in a histogram of the high frequency component amount
and calculating a low frequency percentile value in which the
proportion of the total sum to the sum of incidences counted from
the lower frequency component powers results in a predetermined
proportion in a histogram of the low frequency component amount and
calculating a correction factor based on the high frequency
percentile value and the low frequency percentile value; an
evaluation value calculation part for calculating an evaluation
value by correcting a ratio between the high frequency component
amount and the low frequency component amount by the correction
factor; and a decision part for deciding an awakening level of a
driver based on the evaluation value.
2. The awakening level estimation apparatus for vehicle as defined
in claim 1, wherein the predetermined proportion is between about
70% and about 90%.
3. The awakening level estimation apparatus for vehicle as defined
in claim 1, wherein the correction factor calculation part
calculates a first ratio between a predetermined normal high
frequency percentile value corresponding to a high frequency
percentile value of a normal driver and the calculated high
frequency component percentile value and calculates a second ratio
between a predetermined normal low frequency percentile value
corresponding to a low frequency percentile value of a normal
driver and the calculated low frequency component percentile value
and calculates the correction factor based on the first ratio and
the second ratio.
4. The awakening level estimation apparatus for vehicle as defined
in claim 2, wherein the correction factor calculation part
calculates a first ratio between a predetermined normal high
frequency percentile value corresponding to a high frequency
percentile value of a normal driver and the calculated high
frequency component percentile value and calculates a second ratio
between a predetermined normal low frequency percentile value
corresponding to a low frequency percentile value of a normal
driver and the calculated low frequency component percentile value
and calculates the correction factor based on the first ratio and
the second ratio.
5. The awakening level estimation apparatus for vehicle as defined
in claim 3, wherein the proportion of the normal low frequency
percentile value to the normal high frequency percentile value is
between 2 times and 2.5 times.
6. The awakening level estimation apparatus for vehicle as defined
in claim 4, wherein the proportion of the normal low frequency
percentile value to the normal high frequency percentile value is
between 2 times and 2.5 times.
7. The awakening level estimation apparatus for vehicle as in claim
1, wherein the evaluation value calculation part calculates a ratio
between the high frequency component amount and the low frequency
component amount as the evaluation value in one of the case that
the high frequency percentile value is larger than a predetermined
upper limit value and the case that the high frequency percentile
value is smaller than a predetermined lower limit value.
8. The awakening level estimation apparatus for vehicle as in claim
6, wherein the evaluation value calculation part calculates a ratio
between the high frequency component amount and the low frequency
component amount as the evaluation value in one of the case that
the high frequency percentile value is larger than a predetermined
upper limit value and the case that the high frequency percentile
value is smaller than a predetermined lower limit value.
9. The awakening level estimation apparatus for vehicle as in claim
1, wherein the correction factor calculation part calculates a
correction low frequency percentile value by multiplying the low
frequency percentile value by a ratio between the normal high
frequency percentile value and the high frequency percentile value,
and the evaluation value calculation part calculates a ratio
between the high frequency component amount and the low frequency
component amount as the evaluation value in one of the case that
the correction low frequency percentile value is larger than a
predetermined upper limit value and the case that the correction
low frequency percentile value is smaller than a predetermined
lower limit value.
10. The awakening level estimation apparatus for vehicle as in
claim 8, wherein the correction factor calculation part calculates
a correction low frequency percentile value by multiplying the low
frequency percentile value by a ratio between the normal
high-frequency percentile value and the high frequency percentile
value, and the evaluation value calculation part calculates a ratio
between the high frequency component amount and the low frequency
component amount as the evaluation value in one of the case that
the correction low frequency percentile value is larger than a
predetermined upper limit value and the case that the correction
low frequency percentile value is smaller than a predetermined
lower limit value.
11. The awakening level estimation apparatus for vehicle as in
claim 1, wherein the frequency component power is leveled by
multiplying the frequency component power by a value multiplied by
the frequency component power by a power number n of each
frequency.
12. The awakening level estimation apparatus for vehicle as in
claim 10, wherein the frequency component power is leveled by
multiplying the frequency component power by a value multiplied by
the frequency component power by a power number n of each
frequency.
13. The awakening level estimation apparatus for vehicle as in
claim 1, wherein the evaluation value calculation part calculates a
high frequency component amount based on frequency component powers
excluding a maximum value among the respective frequency component
powers calculated by the frequency component amount calculation
part.
14. The awakening level estimation apparatus for vehicle as in
claim 12, wherein the evaluation value calculation part calculates
a high frequency component amount based on frequency component
powers excluding a maximum value among the respective frequency
component powers calculated by the frequency component amount
calculation part.
15. The awakening level estimation apparatus for vehicle as in
claim 1, wherein the evaluation value calculation part calculates
the evaluation value with time, and the decision part decides that
it is in a situation in which a driver is to be warned in the case
that a value of a counter is increased or decreased in response to
the evaluation value and also the value of the counter reaches a
determination value.
16. The awakening level estimation apparatus for vehicle as in
claim 14, wherein the evaluation value calculation part calculates
the evaluation value with time, and the decision part decides that
it is in a situation in which a driver is to be warned in the case
that a value of a counter is increased or decreased in response to
the evaluation value and also the value of the counter reaches a
determination value.
17. An awakening level estimation method for vehicle, the method
for deciding an awakening level of a driver based on an evaluation
value calculated, comprising: a first step of calculating each
frequency component power by making frequency conversion of a
displacement amount of a vehicle in a direction of vehicle width
detected in a time series manner; a second step of calculating an
average value of the frequency component powers calculated by the
signal processing part as a high frequency component amount; a
third step of calculating a maximum value of the frequency
component powers within a predetermined frequency domain including
a stagger frequency to become apparent in a state in which the
awakening level of the driver decreases as a low frequency
component amount; a fourth step of calculating a high frequency
percentile value in which the proportion of the total sum to the
sum of incidences counted from the lower frequency component powers
results in a predetermined proportion in a histogram of the high
frequency component amount; a fifth step of calculating a low
frequency percentile value in which the proportion of the total sum
to the sum of incidences counted from the lower frequency component
powers results in a predetermined proportion in a histogram of the
low frequency component amount; a sixth step of calculating a
correction factor based on the high frequency percentile value and
the low frequency percentile value; and a seventh step of
calculating an evaluation value by correcting a ratio between the
high frequency component amount and the low frequency component
amount by the correction factor.
18. The awakening level estimation method for vehicle as defined in
claim 17, wherein the predetermined proportion is between about 70%
and about 90%.
19. The awakening level estimation method for vehicle as defined in
claim 17, wherein the sixth step includes a step of calculating a
first ratio between a predetermined normal high frequency
percentile value corresponding to a high frequency percentile value
of a normal driver and the calculated high frequency component
percentile value, a step of calculating a second ratio between a
predetermined normal low frequency percentile value corresponding
to a low frequency percentile value of a normal driver and the
calculated low frequency component percentile value, and a step of
calculating the correction factor based on the first ratio and the
second ratio.
20. The awakening level estimation method for vehicle as defined in
claim 18, wherein the sixth step includes a step of calculating a
first ratio between a predetermined normal high frequency
percentile value corresponding to a high frequency percentile value
of a normal driver and the calculated high frequency component
percentile value, a step of calculating a second ratio between a
predetermined normal low frequency percentile value corresponding
to a low frequency percentile value of a normal driver and the
calculated low frequency component percentile value, and a step of
calculating the correction factor based on the first ratio and the
second ratio.
21. The awakening level estimation method for vehicle as defined in
claim 19, wherein the proportion of the normal low frequency
percentile value to the normal high frequency percentile value is
between 2 times and 2.5 times.
22. The awakening level estimation method for vehicle as defined in
claim 20, wherein the proportion of the normal low frequency
percentile value to the normal high frequency percentile value is
between 2 times and 2.5 times.
23. The awakening level estimation method for vehicle as in claim
17, wherein in the seventh step, a ratio between the high frequency
component amount and the low frequency component amount is
calculated as the evaluation value in one of the case that the high
frequency percentile value is larger than a predetermined upper
limit value and the case that the high frequency percentile value
is smaller than a predetermined lower limit value.
24. The awakening level estimation method for vehicle as in claim
22, wherein in the seventh step, a ratio between the high frequency
component amount and the low frequency component amount is
calculated as the evaluation value in one of the case that the high
frequency percentile value is larger than a predetermined upper
limit value and the case that the high frequency percentile value
is smaller than a predetermined lower limit value.
25. The awakening level estimation method for vehicle as in claim
17, wherein in the sixth step, a correction low frequency
percentile value is calculated by multiplying the low frequency
percentile value by a ratio between the normal high frequency
percentile value and the high frequency percentile value and in the
seventh step, a ratio between the high frequency component amount
and the low frequency component amount is calculated as the
evaluation value in one of the case that the correction low
frequency percentile value is larger than a predetermined upper
limit value and the case that the correction low frequency
percentile value is smaller than a predetermined lower limit
value.
26. The awakening level estimation method for vehicle as in claim
24, wherein in the sixth step, a correction low frequency
percentile value is calculated by multiplying the low frequency
percentile value by a ratio between the normal high frequency
percentile value and the high frequency percentile value and in the
seventh step, a ratio between the high frequency component amount
and the low frequency component amount is calculated as the
evaluation value in one of the case that the correction low
frequency percentile value is larger than a predetermined upper
limit value and the case that the correction low frequency
percentile value is smaller than a predetermined lower limit value.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to an awakening level
estimation apparatus and an awakening level estimation method for
vehicle, and particularly to a technique for estimating an
awakening level of a driver by monitoring a displacement of a
vehicle in a direction of vehicle width in a time series
manner.
[0003] 2. Description of the Related Art
[0004] Development of a technique for preventing an accident caused
by a decrease in an awakening level of a driver is one of important
study problems from the viewpoint of safety, and studies on a
technique for detecting a decrease in an awakening level or a
warning art have been conducted actively. An awakening level
estimation technique capable of accurately deciding an awakening
level even in case that a large change in travel environment or
vehicle speed occurs is disclosed in a JP-A-2002-154345 which is
prior application of an applicant of the present application. In
this estimation technique, displacement amounts of a vehicle in a
direction of vehicle width is first detected in a time series
manner and each frequency component power is calculated by making
frequency conversion of these displacement amounts. Next, an
average value of each of the frequency component powers is
calculated as a high frequency component amount. Together with
that, a maximum value of the frequency component powers within a
predetermined frequency domain including a stagger frequency to
become apparent in a state in which an awakening level of a driver
decreases is calculated as a low frequency component amount. Then,
an awakening level of a driver is decided based-on an evaluation
value corresponding to a ratio of the high frequency component
amount to the low frequency component amount.
[0005] In the conventional art described above, it is decided that
the awakening level of the driver is low in the case that the high
frequency component amount is small and the low frequency component
amount is large. However, there is a personal difference among
drivers in the high frequency component amount and the low
frequency component amount resulting in a criterion of awakening
level estimation. As a result of that, there is a possibility that
an accurate decision on the awakening level becomes difficult in
the case that both of these component amounts are large (a driver
with a large stagger) or the case that both of these component
amounts are small (a driver with a small stagger).
SUMMARY OF THE INVENTION
[0006] The present invention is implemented in view of such
circumstances, and an object of the present invention is to decide
an awakening level of a driver more accurately regardless of a
personal difference among drivers.
[0007] In order to solve such an object, a first invention provides
an awakening level estimation apparatus for vehicle. This
estimation apparatus has a signal processing part for calculating
each frequency component power by making frequency conversion of a
displacement amount of a vehicle in a direction of vehicle width
detected in a time series manner, a frequency component amount
calculation part for calculating an average value of the frequency
component powers calculated by the signal processing part as a high
frequency component amount and also calculating a maximum value of
the frequency component powers within a predetermined frequency
domain including a stagger frequency to become apparent in a state
in which an awakening level of a driver decreases as a low
frequency component amount, a correction factor calculation part
for calculating a high frequency percentile value in which the
proportion of the total sum to the sum of incidences counted from
the lower frequency component powers results in a predetermined
proportion in a histogram of the high frequency component amount
and calculating a low frequency percentile value in which the
proportion of the total sum to the sum of incidences counted from
the lower frequency component powers results in a predetermined
proportion in a histogram of the low frequency component amount and
calculating a correction factor based on the high frequency
percentile value and the low frequency percentile value, an
evaluation value calculation part for calculating an evaluation
value by correcting a ratio between the high frequency component
amount and the low frequency component amount by the correction
factor, and a decision part for deciding an awakening level of a
driver based on the evaluation value.
[0008] Here, in the first invention, the predetermined proportion
is preferably between about 70% and about 90%. Also, the correction
factor calculation part desirably calculates a first ratio between
a predetermined normal high frequency percentile value
corresponding to a high frequency percentile value of a normal
driver and the calculated high frequency component percentile value
and calculates a second ratio between a predetermined normal low
frequency percentile value corresponding to a low frequency
percentile value of a normal driver and the calculated low
frequency component percentile value and calculates the correction
factor based on the first ratio and the second ratio. Further, the
proportion of the normal low frequency percentile value to the
normal high frequency percentile value is preferably between 2
times and 2.5 times.
[0009] Also, in the first invention, the evaluation value
calculation part preferably calculates a ratio between the high
frequency component amount and the low frequency component amount
as the evaluation value in one of the case that the high frequency
percentile value is larger than a predetermined upper limit value
and the case that the high frequency percentile value is smaller
than a predetermined lower limit value.
[0010] Also, in the first invention, the correction factor
calculation part preferably calculates a correction low frequency
percentile value by multiplying the low frequency percentile value
by a ratio between the normal high frequency percentile value and
the high frequency percentile value. In this case, the evaluation
value calculation part desirably calculates a ratio between the
high frequency component amount and the low frequency component
amount as the evaluation value in one of the case that the
correction low frequency percentile value is larger than a
predetermined upper limit value and the case that the correction
low frequency percentile value is smaller than a predetermined
lower limit value.
[0011] Also, in the first invention, the frequency component power
is preferably leveled by multiplying the frequency component power
by a value multiplied by the frequency component power by a power
numbern of each frequency, and more specifically, the power number
n is desirably a value of 2.0 or more to 3.0 or less.
[0012] Also, in the first invention, the evaluation value
calculation part preferably calculates a high frequency component
amount based on frequency component powers excluding a maximum
value among the respective frequency component powers calculated by
the frequency component amount calculation part.
[0013] Also, in the first invention, the evaluation value
calculation part may calculate the evaluation value with time. In
this case, the decision part preferably decides that it is in a
situation in which a driver is to be warned in the case that a
value of a counter is increased or decreased in response to the
evaluation value and also the value of the counter reaches a
determination value. Further, the decision part may vary the amount
of change in the counter in response to the evaluation value.
[0014] A second invention provides an awakening level estimation
method for vehicle, the method for deciding an awakening level of a
driver based on an evaluation value calculated. This estimation
method has a first step of calculating each frequency component
power by making frequency conversion of a displacement amount of a
vehicle in a direction of vehicle width detected in a time series
manner, a second step of calculating an average value of the
frequency component powers calculated by a signal processing part
as a high frequency component amount, a third step of calculating a
maximum value of the frequency component powers within a
predetermined frequency domain including a stagger frequency to
become apparent in a state in which the awakening level of the
driver decreases as a low frequency component amount, a fourth step
of calculating a high frequency percentile value in which the
proportion of the total sum to the sum of incidences counted from
the lower frequency component powers results in a predetermined
proportion in a histogram of the high frequency component amount, a
fifth step of calculating a low frequency percentile value in which
the proportion of the total sum to the sum of incidences counted
from the lower frequency component powers results in a
predetermined proportion in a histogram of the low frequency
component amount, a sixth step of calculating a correction factor
based on the high frequency percentile value and the low frequency
percentile value, and a seventh step of calculating an evaluation
value by correcting a ratio between the high frequency component
amount and the .alpha.1low frequency component amount by the
correction factor.
[0015] Here, in the second invention, the predetermined proportion
is preferably between about 70% and about 90%. Also, the sixth step
may include a step of calculating a first ratio between a
predetermined normal high frequency percentile value corresponding
to a high frequency percentile value of a normal driver and the
calculated high frequency component percentile value, a step of
calculating a second ratio between a predetermined normal low
frequency percentile value corresponding to a low frequency
percentile value of a normal driver and the calculated low
frequency component percentile value, and a step of calculating the
correction factor based on the first ratio and the second ratio. In
this case, the proportion of the normal low frequency percentile
value to the normal high frequency percentile value is desirably
between 2 times and 2.5 times.
[0016] Also, in the seventh step, a ratio between the high
frequency component amount and the low frequency component amount
is preferably calculated as the evaluation value in one of the case
that the high frequency percentile value is larger than a
predetermined upper limit value and the case that the high
frequency percentile value is smaller than a predetermined lower
limit value.
[0017] Also, in the sixth step, a correction low frequency
percentile value may be calculated by multiplying the low frequency
percentile value by a ratio between the normal high frequency
percentile value and the high frequency percentile value. In this
case, in the seventh step, a ratio between the high frequency
component amount and the low frequency component amount is
preferably calculated as the evaluation value in one of the case
that the correction low frequency percentile value is larger than a
predetermined upper limit value and the case that the correction
low frequency percentile value is smaller than a predetermined
lower limit value.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] FIGS. 1A and 1B are each a distribution characteristic
diagram of frequency component amounts in a situation in which a
driver with a small stagger is sleepy;
[0019] FIGS. 2A and 2B are each a distribution characteristic
diagram of frequency component amounts in a situation in which a
driver with a large stagger is not sleepy;
[0020] FIG. 3 is a block configuration diagram of an awakening
level estimation apparatus;
[0021] FIG. 4 is a flowchart of an evaluation value calculation
routine;
[0022] FIG. 5 is a diagram showing a change in a lateral
displacement amount with time;
[0023] FIG. 6 is a diagram showing each frequency component
power;
[0024] FIG. 7 is an explanatory diagram of evaluation value
calculation;
[0025] FIG. 8 is a flowchart of a correction factor calculation
routine;
[0026] FIG. 9 is an explanatory diagram of a high frequency
percentile value;
[0027] FIG. 10 is a flowchart of a warning determination routine;
and,
[0028] FIG. 11 is a diagram showing an actual measured result at
the time of freeway travel.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0029] An overview of an estimation technique of an awakening level
according to the present embodiment will be first described with
reference to FIGS. 1 and 2 prior to specific description of an
awakening level estimation apparatus. FIGS. 1A and 1B are one
example of a distribution characteristic diagram of frequency
component amounts in a situation in which a driver with a small
stagger is sleepy, and FIGS. 2A and 2B is one example of a
distribution characteristic diagram of frequency component amounts
in a situation in which a driver with a large stagger is not
sleepy. In these diagrams, the axis of abscissa shows a high
frequency component amount and the axis of ordinate shows a low
frequency component amount.
[0030] Black circle points shown in the drawing plot coordinate
points (frequency component amount points) represented by high
frequency component amounts calculated with certain timing and low
frequency component amounts calculated with the same timing as this
timing. Here, the "frequency component amount" means discrete
frequency component power obtained by making frequency conversion
of a displacement amount of a vehicle in a direction of vehicle
width detected in a time series manner. In a normal travel state,
intentional steering caused by a curve etc. is performed, so that
component amounts of the relatively high frequency side (high
frequency component amounts) tend to stationarily appear over the
whole of frequency domains regardless of an awakening state of a
driver. In the embodiment, an average value of the frequency
component powers calculated is used as the "high frequency
component amount". On the contrary, component amounts of the
relatively low frequency side (low frequency component amounts)
tend to become apparent only in a travel state in which an
awakening level decreases. In the embodiment, a maximum value of
the frequency component powers within a predetermined frequency
domain is used as the "low frequency component amount". This
frequency domain, which is set with reference to a stagger
frequency described below, is a low frequency band including a
stagger frequency.
[0031] An area surrounded by an ellipse is an area having a great
influence on awakening level estimation, that is, an area in which
the high frequency component amount is small and the low frequency
component amount is large. The number of frequency component amount
points present within the ellipse area increases as an awakening
level of a driver decreases. A value obtained by dividing the low
frequency component amount by the high frequency component amount
(P'slp/P'ave described below) increases as the awakening level of
the driver decreases.
[0032] Consider an awakening state in a situation in which a driver
with a small stagger is sleepy as shown in FIGS. 1A and 1B. FIG. 1A
shows a distribution characteristic in which the calculated
frequency component amount points (high frequency component
amounts, low frequency component amounts) are plotted as they are.
As a characteristic of a driver of this type, the low frequency
component amount is essentially small as compared with a
characteristic of a normal driver. Because of that, there are cases
where the frequency component amount points do not quite appear
within the area surrounded by the ellipse even under travel in
which an awakening level decreases. As a result of that, there is a
possibility that it is wrongly determined that the awakening level
does not decrease regardless of a state in which the awakening
level decreases.
[0033] On the other hand, consider an awakening state in a
situation in which a driver with a large stagger is not sleepy as
shown in FIGS. 2A and 2B. FIG. 2A shows a distribution
characteristic in which the calculated frequency component amount
points (high frequency component amounts, low frequency component
amounts) are plotted as they are. As a characteristic of a driver
of this type, the low frequency component amount is essentially
large as compared with a characteristic of a normal driver. Because
of that, there are cases where many frequency component amount
points appear within the area surrounded by the ellipse even under
travel in which an awakening level does not decrease. As a result
of that, there is a possibility that it is wrongly determined that
the awakening level decreases regardless of a state in which the
awakening level does not decrease.
[0034] A cause of occurrence of the wrong determination in the two
cases described above is the point that intrinsic characteristics
of individual drivers about a stagger are not taken into account.
The intrinsic characteristic of the driver is reflected on a low
frequency percentile value and a high frequency percentile value.
White square points shown in FIGS. 1 and 2 plot coordinate points
(percentile points) represented by high frequency percentile values
calculated with certain timing and low frequency percentile values
calculated with the same timing as this timing. There is a high
correlation between percentile points (high frequency percentile
values, low frequency percentile values) calculated with certain
timing and frequency component amount points (high frequency
component amounts, low frequency component amounts) calculated with
the same timing as this timing. Here, the "high frequency
percentile value" is a percentile value in which the proportion of
the total sum to the sum of incidences counted from the lower
frequency component powers results in a predetermined proportion in
a histogram of the high frequency component amount. In one travel
process performed by one driver, variations in the high frequency
percentile value are relatively small and tend to become an
approximately constant value (and hardly depend on an awakening
state of the driver).
[0035] Incidentally, in the embodiment, the predetermined
proportion is set to 80% and a 80 percentile value (80%ile value)
is used, but this proportion is one example and may be within the
range of between about 70% and about 90% (similar ratio applies to
the next low frequency percentile value). On the other hand, the
"low frequency percentile value" is a percentile value (for
example, 80%ile value) in which the proportion of the total sum to
the sum of incidences counted from the lower frequency component
powers results in a predetermined proportion (for example, 80%) in
a histogram of the low frequency component amount. This low
frequency percentile value is different from the high frequency
percentile value in characteristics, and variations are large and
the variations tend to increase as an awakening level decreases.
Incidentally, a ratio of the high frequency percentile value to the
low frequency percentile value tends to become an approximately
constant value as long as a driver is awake.
[0036] An inventor performed experiments on many drivers and
studied travel data obtained in detail, with the result that it was
proved that a percentile point (a high frequency percentile value,
a low frequency percentile value) of a normal driver (a virtual
driver showing the travel characteristic with the highest
incidence) was (200, 400 to 500). Hereinafter, the high frequency
percentile value of the normal driver is called "a normal high
frequency percentile value" and is set to 200 in the embodiment.
Also, the low frequency percentile value of the normal driver is
called "a normal low frequency percentile value" and is set to 500
in the embodiment. Then, the percentile point of the normal driver
is called "a normal percentile point". Incidentally, the proportion
of the normal low frequency percentile value to the normal high
frequency percentile value may be within the range of between 2
times and 2.5 times and, for example, the normal percentile point
may be set to (200, 400).
[0037] In the case shown in FIG. 1A, it is found that the
percentile points (high frequency percentile values, low frequency
percentile values) concentrate in the vicinity of (100, 250).
Therefore, in view of the fact that the percentile point of the
normal driver is (200, 500), it can be decided that a driver with a
characteristic shown in FIG. 1A is a driver with a small stagger
essentially. On the other hand, in the case shown in FIG. 2A, it is
found that the percentile points concentrate in (100 to 200, 400 to
600). Therefore, in view of the fact that the percentile point of
the normal driver is (200, 500), it can be decided that a driver
with a characteristic shown in FIG. 2A is a driver with a large
stagger essentially.
[0038] Hence, in the embodiment, frequency component amount points
are normalized by shifting the respective frequency component
amount points by an aspect ratio between the percentile points and
the normal percentile points calculated. For example, consider a
certain frequency component amount point (100, 500) in FIG. 1A. In
this case, when it is assumed that a percentile point corresponding
to this frequency component amount point is (100, 250), an aspect
ratio between this and a normal percentile point (200, 500) results
in (width 2.0 times, length 2.0 times). As a result of that,
coordinates after the shift of this frequency component amount
point result in (100.times.2.0, 500.times.2.0), namely (200, 1000).
By performing such a shift with respect to all the frequency
component amount points, a distribution characteristic shown in
FIG. 1A is corrected to a distribution characteristic shown in FIG.
1B. Through such a correction, many frequency component amount
points appear within the area surrounded by the ellipse, so that a
wrong determination about a driver with a small stagger essentially
can be prevented effectively.
[0039] Also, a similar shift is performed with respect to a
distribution characteristic shown in FIG. 2A. For example, consider
a certain frequency component amount point (100, 1000) in FIG. 2A.
In this case, when it is assumed that a percentile point
corresponding to this frequency component amount point is (100,
500), an aspect ratio between this and a normal percentile point
(200, 500) results in (width 2.0 times, length 1.0 times). As a
result of that, coordinates after the shift of this frequency
component amount point result in (100.times.2.0, 1000.times.1.0),
namely (200, 1000). By performing such a shift with respect to all
the frequency component amount points, the distribution
characteristic shown in FIG. 2A is corrected to a distribution
characteristic shown in FIG. 2B. Through such a correction, the
number of frequency component amount points appearing within the
area surrounded by the ellipse decreases, so that a wrong
determination about a driver with a large stagger essentially can
be prevented effectively.
[0040] In this manner, the high frequency component amount and the
low frequency component amount are corrected by the aspect ratio
between the percentile point and the normal percentile point
calculated. Thus, all the drivers can be handled in a manner
similar to a normal driver regardless of a personal difference
among drivers about a stagger. As a result of that, an awakening
level of the driver can be decided more accurately.
[0041] Next, a vehicle awakening level estimation apparatus in the
embodiment will be described with reference to FIG. 3. A lateral
displacement detection part 1 detects a displacement (lateral
displacement) of a vehicle in a direction of vehicle width. For
example, a monocular camera or a stereo camera using a CCD
(charge-coupled device) etc. can be used in this detection part 1.
An image information processing part 2 processes an image obtained
by the lateral displacement detection part 1 and finds a
displacement amount of the vehicle. For example, images of right
and left lanes of a road are picked up by the CCD and image data of
one frame is stored in memory of the image information processing
part 2. Then, the right and left lanes are respectively recognized
using an image recognition technique. In this recognition process,
an area corresponding to the lanes is identified by the image data
of one frame using well-known recognition techniques such as stereo
matching or a template about the lane. A vehicle position within
the right and left lanes can be computed from, for example, a road
width and a distance from the center of the vehicle in a lateral
direction to the center of the right and left lanes.
[0042] Incidentally, the lateral displacement detection part 1 can
also detect the lateral displacement by combining a vehicle speed
with a GPS and navigation system or communication between road
vehicles based on a magnetic coil buried in a road in addition to a
self-contained detection device such as a camera (see JP-A-9-99756
with respect to a stagger warning using navigation) Further, since
the lateral displacement can be estimated by a steering angle, a
steering angle sensor may be used as the lateral displacement
detection part 1. Also, the lateral displacement may be estimated
by detecting a yaw rate or lateral acceleration. A lateral stagger
(displacement amount) of the vehicle is measured, for example, with
a resolution of 1 mm and a time step of 0.1 seconds. Data about the
displacement amount is stored in a shift register 3 at any time. A
sequence of displacement amount data calculated in a time series
manner is stored by predetermined time. The data stored in the
shift register 3 is sequentially updated with calculation and
storage of new displacement amount data.
[0043] An FFT signal processing part 4, a frequency component
amount calculation part 5, a correction factor calculation part 7,
an evaluation value calculation part 8 and a decision part 9 are
functional blocks implemented by a general computer mainly
comprising a CPU, RAM, ROM and an input/output circuit. Under
control of an application for executing a routine described below,
each member constructing the computer interacts and thereby the
functional blocks 4, 5, 7 to 9 are implemented. Incidentally, an
awakening level estimation program, lower limit values .alpha.1low,
.alpha.2'low and upper limit values .alpha.1high, .alpha.2'high in
a correction factor calculation routine, a normal value in
correction factor calculation, a lower limit value Plow of a high
frequency component amount P'ave, a table for setting of a step
value .beta. and warning determination values D1, D2, etc. are
stored in the ROM.
[0044] FIG. 4 is a flowchart of an evaluation value calculation
routine and this routine is executed repeatedly at predetermined
intervals. First, in step 1, the FFT signal processing part 4 reads
out displacement amount data for the past X seconds stored in the
shift register 3 every Y seconds (for example, 90 seconds or
shorter). In the sample time X, a long time (for example, the order
of 50 to 80 seconds) is preferably set to a certain extent in order
to estimate an awakening level with high accuracy.
[0045] In step 2, the FFT signal processing part 4 makes frequency
conversion of displacement amounts detected in a time series manner
using a fast Fourier transformation (FFT) etc. and calculates each
frequency component power (amplitude) P[i] in a frequency spectrum.
In the embodiment, 16 frequency component powers P[1] to P[16] are
calculated in increments of 0.02 [Hz] in a frequency domain of 0.03
to 0.3 [Hz]. The reason why a frequency domain lower than 0.03 Hz
is not taken into account is because the power of its domain tends
to increase at the time of curve travel and directly has nothing to
do with an awakening level of a driver. Also, the reason why a
frequency domain higher than 0.3 Hz is not taken into account is
because an operation amount necessary for calculation of an
evaluation value H is decreased since the power within its
frequency domain is generally small to a negligible extent.
[0046] Here, a relation between the displacement amount and the
frequency component power will be described. FIG. 5 is a diagram
showing a relation between elapsed time from a driving start and a
change in a lateral displacement amount. These are measured results
of the cases of assuming that a relatively wide-open automotive
special-purpose road is traveled in a relatively monotonous travel
environment. After about 10 minutes of travel, it is in a state
immediately after joining to a main road and going with a stream of
traffic to travel, and the displacement amount is still small.
After about 20 minutes have elapsed, it is accustomed to the travel
environment and becomes a relaxing state and the displacement
amount of a low frequency component increases more than the case
immediately after the travel start and a high frequency component
decreases. After about 50 minutes have elapsed, it becomes a state
of tedious driving or having a slightly sleepy feeling and a
tendency in which a large displacement amount sometimes occurs is
shown. In this case, a tendency in which the displacement amount of
the low frequency component increases becomes more remarkable as
compared with the case of a lapse of 20 minutes.
[0047] FIG. 6 is a diagram showing a relation between a frequency
component i and its power P[i] by making frequency conversion of
the displacement amount at each the elapsed time of FIG. 5 and is a
diagram represented by connecting each of the discrete frequency
component powers P[i] in a line graph manner. A dotted line shows
each of the frequency component powers P[i] after about 10 minutes
of travel and a broken line shows the powers P[i] after about 20
minutes and a solid line shows the powers P[i] after a lapse of
about 50 minutes, respectively. From this diagram, it is found that
there is a tendency in which the frequency component powers P[i] of
a low frequency domain increase as travel time lengthens.
[0048] In step 3, the frequency component amount calculation part 5
levels each of the frequency component powers P[i] in frequency
domains (i=1 to 16) of 0.03 to 0.3 [Hz] according to the following
formula and calculates frequency component powers P'[i]
leveled.
[0049] [Mathematical Formula 1]
[0050] P'[i]=P[i].multidot.f.sup.n
[0051] (power number n :2.0.ltoreq.n.ltoreq.3.0)
[0052] In the case of considering that a stagger of a vehicle
inside a lane is one of many fluctuations present in the natural
world, its amplitude is 1/f and the power results in 1/f.sup.2.
Therefore, a power number n in the mathematical formula 1 may be
2.0 theoretically, but is preferably set to n=2.5 from an
experimental result. This is probably due to specifications of a
vehicle, a personal difference among drivers about driving or an
influence of a travel road. However, an awakening level of a driver
can be decided even using an arbitrary power number in the range of
2.0 to 3.0. In the embodiment, 2.5 is used as the power number
n.
[0053] FIG. 7 is a diagram showing a relation between the frequency
components i and the leveled frequency component powers P'[i]. From
distribution of the leveled frequency component powers P'[i], a
general characteristic can be checked visually. From the same
diagram, it is found that the power P'[4] of 0.09 [Hz] and the
power P'[5] of 0.11 [Hz] in the vicinity of 0.1 [Hz] which is a low
frequency domain, particularly a stagger frequency f1 suddenly
increase after about 50 minutes. In a state in which an awakening
level of a driver decreases, the power in the vicinity of the
stagger frequency f1 tends to become apparent with respect to a
lateral displacement of a vehicle. In other words, in the state in
which the awakening level decreases, it has a feature that only the
power of the low frequency domain including the stagger frequency
f1 increases and a level other than the low frequency domain
decreases. In view of such a tendency, the awakening level of the
driver can be decided by comparing the peak of the power in the
vicinity of the stagger frequency f1 with power states of frequency
domains other than the stagger frequency.
[0054] Here, "the stagger frequency f1" means a frequency to become
apparent (or converge) in the state in which the awakening level of
the driver decreases (including a doze state). Generally, the
stagger frequency tends to appear at about 0.08 to 0.12 [Hz] in a
passenger vehicle, but is influenced by a response delay in vehicle
behavior with steering operation, vehicle characteristics, a
vehicle speed, etc. actually, so that a proper value is set every
vehicle model through experiment or simulation. In the embodiment,
the stagger frequency f1 is set to 0.01 [Hz].
[0055] In step 4 subsequent to step 3, the frequency component
amount calculation part 5 obtains the total sum of each of the
frequency component powers P'[1] to P'[16] and calculates its
average value as a high frequency component amount P'ave. However,
in the embodiment, in order to reflect the awakening level of the
driver on the evaluation value H more accurately, the maximum power
among each of the frequency component powers P'[1] to P'[16] is
excluded and the high frequency component amount P'ave is
calculated from the remaining frequency component powers P'[i]. The
reason why such filtering is performed is because an influence of
an increase in power of the stagger frequency f1 and an influence
of disturbance are eliminated.
[0056] In step 5, the frequency component amount calculation part 5
makes a determination of stagger frequency power, that is, compares
sizes of the frequency component powers P'[4] and P'[5] in a
predetermined frequency domain (0.09 to 0.11 [Hz]) including the
stagger frequency f1 (0.1 [Hz]). Then, the larger frequency
component power is set as a low frequency component amount P'slp.
That is, when the power P'[5] of 0.11 [Hz] is larger than the power
P'[4] of 0.09 [Hz], the power P'[5] is set as the low frequency
component amount P'slp (step 6). On the other hand, when the power
P'[4] of 0.09 [Hz] is larger than or equal to the power P'[5] of
0.11 [Hz], the power P'[4] is set as the low frequency component
amount P'slp (step 7). Then, a set of the high frequency component
amount P'ave and the low frequency component amount P'slp
calculated in steps 4 to 7 is stored in a shift register 6.
[0057] In step 8, the correction factor calculation part 7
calculates a correction factor K2 based on the high frequency
component amount P'ave and the low frequency component amount
P'slp. FIG. 8 is a flowchart of a correction factor calculation
routine and this routine is executed repeatedly at predetermined
intervals. First, in step 21, the correction factor calculation
part 7 acquires a history of the high frequency component amount
P'ave stored in the shift register 6. In the embodiment, the number
of histories of the high frequency component amount P'ave acquired
is set to 500 samples as one example.
[0058] In step 22, the correction factor calculation part 7
calculates a high frequency percentile value .alpha.1 based on the
high frequency component amount P'ave. FIG. 9 is an explanatory
diagram of the high frequency percentile value .alpha.1. First, the
correction factor calculation part 7 creates a histogram of the
high frequency component amount P'ave by the samples acquired.
Next, in this histogram, a value in which the proportion of the
total sum to the sum of incidences counted from the lower frequency
component powers results in a predetermined proportion is set to
the high frequency percentile value .alpha.1. In the embodiment,
this proportion is set to 80% and a 80 percentile value of the high
frequency component amount P'ave is calculated. In other words, the
value .alpha.1 calculated thus is a threshold value of 80% from the
lower frequency component powers. By this threshold value, an
abnormal value in the histogram is eliminated and a main data range
in this histogram can be approximated to normal distribution.
[0059] In step 23, the correction factor calculation part 7
acquires a history of the low frequency component amount P'slp
stored in the shift register 6. In the embodiment, the number of
histories of the low frequency component amount P'slp acquired is
set to 500 samples as one example.
[0060] In step 24, the correction factor calculation part 7
calculates a low frequency percentile value .alpha.2 based on the
low frequency component amount P'slp. First, the correction factor
calculation part 7 creates a histogram of the low frequency
component amount P'slp by the samples acquired. Next, in this
histogram, it is counted from the lower frequency component powers
and a 80 percentile value of the low frequency component amount
P'slp is set to the low frequency percentile value .alpha.2.
[0061] In step 25, the correction factor calculation part 7 decides
whether or not the high frequency percentile value .alpha.1 is
normal. That is, it decides whether or not this value .alpha.1 is
larger than a predetermined lower limit value .alpha.1low (for
example, 100) or this value .alpha.1 is larger than a predetermined
upper limit value .alpha.1high (for example, 300). When the high
frequency percentile value .alpha.1 is within the range from the
lower limit value .alpha.1low to the upper limit value
.alpha.1high, the flowchart proceeds to step 27. On the contrary,
when the high frequency percentile value .alpha.1 is smaller than
the lower limit value .alpha.1low or is larger than the upper limit
value .alpha.1high, it is decided that the high frequency
percentile value .alpha.1 is not normal, and the flowchart proceeds
to step 26. The reason why such a threshold value is provided is
because when the high frequency percentile value .alpha.1 is not
within the range of these values, an influence of a factor (for
example, an influence of an environmental factor) other than a
personal difference among drivers is large and it is improper as
data corrected to a normal driver. That is, in the case that the
high frequency percentile value .alpha.1 is smaller than the lower
limit value .alpha.1low, when a correction is made to such a
driver, there is a high possibility of wrongly determining that an
awakening level decreases. Also, in the case that the high
frequency percentile value .alpha.1 is larger than the upper limit
value .alpha.1high, there is a high possibility that a stagger of a
vehicle occurs in a state in which the stagger is not recognized
accurately or at the time of starting to enter a freeway.
[0062] In step 26, 1 is set as the correction factor K2. This means
that in step 11 of calculating the evaluation value H described
below, without correcting a value of P'slp/P'ave, this value is set
to the evaluation value H as it is.
[0063] On the other hand, in step 27, the correction factor
calculation part 7 calculates K1 which is a ratio between the high
frequency percentile value .alpha.1 and a predetermined normal high
frequency percentile value. This normal high frequency percentile
value is a value corresponding to the high frequency percentile
value .alpha.1 of a normal driver and is set to 200 in the
embodiment. Next, in step 28, the correction factor calculation
part 7 calculates a correction low frequency percentile value
.alpha.2' by multiplying the low frequency percentile value
.alpha.2 by the ratio K1 calculated in step 27.
[0064] In step 29, the correction factor calculation part 7 decides
whether or not the correction low frequency percentile value
.alpha.2' is normal. That is, it decides whether or not this value
.alpha.2' is larger than a predetermined lower limit value
.alpha.2.sup.1 low (for example, 400) or this value .alpha.2' is
larger than a predetermined upper limit value .alpha.2'high (for
example, 500). When the correction low frequency percentile value
.alpha.2' is within the range from the lower limit value
.alpha.2'low to the upper limit value .alpha.2'high, the flowchart
proceeds to step 30. On the contrary, when the correction low
frequency percentile value .alpha.2' is smaller than the lower
limit value .alpha.2'low or is larger than the upper limit value
.alpha.2'high, it is decided that the correction low frequency
percentile value .alpha.2' is not normal, and the flowchart
proceeds to step 26. The reason why such a threshold value is
provided is because when the correction low frequency percentile
value .alpha.2' is not within the range of these values, an
influence of a factor other than a personal difference among
drivers is large and it is improper as data corrected to a normal
driver. That is, in the case that the correction low frequency
percentile value .alpha.2' is smaller than the lower limit value
.alpha.2'low, when a correction is made to such a driver, there is
a high possibility of wrongly determining that an awakening level
decreases. Also, in the case that the correction low frequency
percentile value .alpha.2' is larger than the upper limit value
.alpha.2'high, it is in a state in which a decrease in an awakening
level of a driver continues.
[0065] In step 26, 1 is set as the correction factor K2. This means
that in step 11 of calculating the evaluation value H described
below, without correcting a value of P'slp/P'ave, this value is set
to the evaluation value H as it is in a manner similar to the case
of step 26.
[0066] In step 30, the correction factor calculation part 7
calculates the correction factor K2 based on the correction low
frequency percentile value .alpha.2'. This correction factor K2 is
calculated as a ratio between the corrected low frequency
percentile value .alpha.2' and a predetermined normal low frequency
percentile value. This normal low frequency percentile value is a
value corresponding to the low frequency percentile value .alpha.2
of a normal driver and is set to 500 in the embodiment.
[0067] Incidentally, the correction factor K2 calculated thus is
calculated by steps 25 to 30 in order to decide whether or not the
high frequency percentile value .alpha.1 and the correction low
frequency percentile value .alpha.2' are normal. However, in the
case of only calculating its value, the value may be calculated by
the following procedure. First, a first ratio which is a ratio
between a normal high frequency percentile value and the high
frequency percentile value .alpha.1 is calculated. Next, a second
ratio which is a ratio between a normal low frequency percentile
value and the low frequency percentile value .alpha.2 is
calculated. Then, the correction factor K2 can be calculated by
totaling the first ratio and the second ratio calculated thus.
[0068] In step 9, the evaluation value calculation part 8
determines a lower limit of the high frequency component amount
P'ave, that is, decides whether or not the high frequency component
amount P'ave is smaller than a preset lower limit value Plow (for
example, 100). When the high frequency component amount P'ave is
smaller than the lower limit value Plow, it is decided that an
awakening state of a driver is stable, and the high frequency
component amount P'ave is set to the lower limit value Plow (step
10). As a result of this, in the case of calculation of the
evaluation value H in step 11, a situation in which a denominator
becomes too small and the evaluation value H becomes large
improperly is prevented (an increase in the evaluation value H
means a decrease in the awakening level). On the contrary, when the
high frequency component amount P'ave is larger than or equal to
the lower limit value Plow, step 10 is skipped and the flowchart
proceeds to step 11.
[0069] In step 11, the evaluation value calculation part 8
calculates the evaluation value H based on the following formula.
This evaluation value H corresponds to an instantaneous awakening
level without consideration of a factor with time, and is
calculated by correcting a ratio between the high frequency
component amount P'ave and the low frequency component amount P'slp
by the correction factor K2. Incidentally, as described above, in
the case of determining that the high frequency percentile value
.alpha.1 and the correction low frequency percentile value
.alpha.2' are abnormal, 1 is set to the correction factor K2 in
step 26. The evaluation value H calculated in this case corresponds
to an evaluation value H calculated without being corrected by the
correction factor K2. Then, after the evaluation value H is
calculated in step 11, the present routine exits.
[0070] [Mathematical Formula 2]
[0071] H=(P'slp.times.K2)/P'ave.times.100
[0072] As shown in FIG. 7, in a state in which a driver is awake
(after a lapse of about 10 minutes), the low frequency component
amount P'slp (P'[4]) or P'[5]) is small, so that the evaluation
value H becomes a small value. On the contrary, in a state in which
an awakening level of a driver decreases (after a lapse of about 50
minutes), the low frequency component amount P'slp increases, so
that a value of the evaluation value H becomes large. Thus, the
evaluation value H results in a value reflecting the awakening
level of the driver.
[0073] FIG. 10 is a flowchart of a warning determination routine
and this routine is executed repeatedly at predetermined intervals.
First, in step 31, the decision part 9 sets constants .beta.1 to
.beta.8, 0 as step values .beta. from the following table based on
the evaluation value H calculated in an evaluation value
calculation routine which is another routine. Incidentally, these
constants have a non-linear relation equipped with
.vertline..beta.1.vertline.>.vertline..beta.2.vertline.&-
gt;.vertline..beta.3.vertline.>.vertline..beta.4.vertline.>.vertline-
..beta.5.vertline.,
.vertline..beta.6.vertline.<.vertline..beta.7.vertl-
ine.<.vertline..beta.8.vertline. since the amount of change in
an awakening level counter D is varied in response to a value of
the evaluation value H.
[0074] (Setting of step values)
1 Evaluation value H Step value .beta. >1000 +.beta.1 >900
+.beta.2 >800 +.beta.3 >500 +.beta.4 >400 +.beta.5 >300
.+-.0 >200 -.beta.6 >100 -.beta.7 >0 -.beta.8
[0075] Next, in step 32, the decision part 9 updates a value of the
awakening level counter D by adding the step value .beta. to the
current value of the awakening level counter D or subtracting the
step value .beta. from the current value. Then, in step 33, a
primary warning determination is made, that is, it is decided
whether or not the awakening level counter D is larger than or
equal to a first determination value D1. If not in this step 33, it
is decided that a driver is in an awakening state, and the present
routine exits. On the other hand, when the awakening level counter
D is larger than or equal to the first determination value D1, it
is decided that there is a need to urge an awakening on the driver,
and the flowchart proceeds to step 34.
[0076] In step 34, a secondary warning determination is made, that
is, it is decided whether or not the awakening level counter D is
larger than or equal to a second determination value D2. If not in
this step 34, in order to give a warning of a stagger of a vehicle
due to a decrease in an awakening level of a driver, the present
routine exits after giving a primary warning to a warning part 10
(step 35). On the other hand, if so in step 34, in order to give a
warning of a doze state in which the awakening level of the driver
decreases further, the present routine exits after giving secondary
warning processing to the warning part 10 (step 36).
[0077] The warning part 10 receives instructions from the decision
part 9 and performs various warning processing for urging an
awakening on the driver. As the warning processing, various cases
are considered and as one example, a case of sounding a collision
warning is given. That is, when it is decided that the awakening
level decreases, a warning distance between vehicles is set to a
longish distance than usual (early timing). Also, the warning part
10 may sound a deviation warning. For example, timing constructed
so as to sound at the instant of treading on a lane is early set at
the time of a decrease in the awakening level. Further, a doze
warning may be sounded. For example, at the time of a decrease in
the awakening level, "stagger caution" is displayed on a display
screen along with a stagger warning beep.
[0078] FIG. 11 is a diagram showing an actual measured result at
the time of freeway travel, and the lower portion shows a
characteristic of a lateral displacement of a vehicle and the upper
portion shows a characteristic of the evaluation value H and the
middle portion shows a characteristic of the awakening level
counter D, respectively. In the vicinity of a lapse of 1400 seconds
since a travel start, the characteristic peaks continuously appear
in the lateral displacement of the vehicle and the stagger
frequency f1 of 0.1 [Hz] becomes apparent. As a result of this, the
evaluation value H increases and a value of the awakening level
counter D is incremented, so that a warning to a driver is given
properly. Incidentally, depending on a measurement situation, the
peak of the evaluation value H singly appears even before a lapse
of 1400 seconds. However, in the embodiment, the warning to the
driver is not given unless such peaks continuously appear (in other
words, unless the awakening level counter D is continuously
incremented).
[0079] Thus, in the embodiment, varying sizes of a value of the
high frequency component amount P'ave and a value of the low
frequency component amount P'slp caused by a personal difference
among drivers can be solved by correcting the evaluation value H by
the correction factor K2. Therefore, various drivers as shown in
FIGS. 1 and 2 can be handled as a normal driver, so that a problem
of a wrong determination caused by the personal difference among
drivers can be solved and an awakening level of the driver can be
decided more accurately.
[0080] Also, in the embodiment, in the case of deciding that the
high frequency percentile value .alpha.1 and the correction low
frequency percentile value .alpha.2' are not normal, a correction
by the correction factor K2 is not made (corresponding to K2=1) and
the evaluation value His calculated. Since the evaluation value H
is calculated thus, when influences of an environmental factor etc.
are large, a problem that these influences are also corrected and
the evaluation value H is calculated can be solved.
[0081] Also, in the embodiment, an awakening level of a driver is
decided by comparing the peak of the power in the vicinity of the
stagger frequency f1 with the powers of frequency domains other
than the stagger frequency. Therefore, there is no need to
previously prepare samples at the time of normal driving and based
on only data (including the just previous data) at the time of
determination, the awakening level of the driver can be decided. As
a result of that, without depending on a change in travel
environment, the awakening level can be determined properly and a
problem of a wrong determination caused by the change in travel
environment as described in the conventional art can be solved.
[0082] Also, the evaluation value H is calculated after a lower
limit value is set with respect to a level of the high frequency
component amount P'ave described above. As a result of this, a
situation in which a denominator in the mathematical formula 2 used
as a calculation formula of the evaluation value H becomes too
small by P'ave is prevented, so that the awakening level can be
estimated accurately without being influenced by a driving pattern
specific to a driver or slight disturbance at the time of
high-speed travel.
[0083] Also, in the embodiment, when the peak of the power within a
frequency domain including the stagger frequency f1 becomes more
apparent than that of the powers of frequency domains other than
the stagger frequency due to a stagger of the lateral displacement
of the vehicle, a decrease in the awakening level of the driver is
detected. In such a detection technique, even when a situation in
which a lateral displacement amount is generally small or a slight
side wind or a situation of passing by a large-size vehicle occurs
at the time of stable high-speed travel, a wrong determination of
the awakening level can be prevented.
[0084] Further, conventionally, by performing time averaging of a
single awakening level and calculating the final awakening level
and comparing its value with a threshold value for warning
determination, it has been decided whether or not to give a
warning. However, in such a conventional technique, there is a
problem that a time delay in the warning occurs. On the contrary,
in a counter method as described in the embodiment, the step value
.beta. of the awakening level counter D is increased in the case
that the evaluation value H corresponding to a single awakening
level is large (particularly, the case that an awakening state
decreases remarkably). Therefore, a warning can be given without
delay as compared with time averaging processing used as a linear
counter.
[0085] In the present invention thus, various drivers can be
handled as a normal driver by correcting an evaluation value by a
correction factor. As a result of this, a wrong determination
caused by a personal difference among drivers can be solved and an
awakening level of a driver can be decided more accurately.
[0086] The disclosure of Japanese Patent Application No.
2002-308086 filed on Oct. 23, 2002 including the specification,
drawings and abstract is incorporated herein by reference in its
entirety.
[0087] While the presently preferred embodiments of the present
invention have been shown and described, it is to be understood
that these disclosures are for the purpose of illustration and that
various changes and modifications may be made without departing
from the scope of the present invention as set forth in the
appended claims.
* * * * *